This invention relates to missile control systems and more particularly to electro-pneumatic control valves for controlling the actuators which drive generally, either missile control surfaces or gimbaled motor nozzles.
All missiles and space vehicles use control systems to change the vehicle's flight path. Typically, they use actuators that rotate aerodynamic control fins or, alternately, that rotate gimbaled thrust vector control nozzles. Typically, the actuators are driven by electrical, hydraulic, or pneumatic power. Studies show cold gas-powered actuators to be superior in cost, weight, size and complexity to the other alternatives for actuation of tactical missile control fins and motor nozzles. However, prior art pneumatic actuator bandwidth has typically ranged from 15 to 25 Hz for applications requiring 0.5 to 2.0 horsepower, while new tactical missile applications require bandwidths in the 30 to 45 Hz range.
Generally there are unbalanced piston actuator systems and balanced piston actuator systems as shown in FIGS. 1 and 2 respectively. An examination of FIGS. 1 and 2 shows that the unbalanced piston actuator scheme required two valves to drive the single fin, whiel the balanced piston actuator required 4 valves. Typically, the valves employed were solenoid-operated poppet valves which are not pressure-balanced and thus require an increased solenoid force-stroke product with increasing actuating horsepower. The result is a degradation of valve response and actuator bandwidth with increasing horsepower. Typically, 16 control solenoids and drive electronic circuits were required per missile to drive the balanced piston scheme, which clearly raises questions about control system reliability. In contrast, the unbalanced piston system required only 8 solenoids and drive circuits per missile. It is important to note that the balanced piston actuator is inherently four times stiffer than the unbalanced piston actuator and capable of twice the horsepower for comparable actuator size.
Attempts to exploit the advantages of the balanced piston actuator to date have met with only modest success, one of the reasons being the requirement of 16 control solenoids and drive circuits when using the solenoid-operated poppet valves, as discussed. Clearly there have been attempts to replace the poppet valves with compound valves, although the fluid medium has been hydraulic rather than pneumatic. The NIKE missile, designed and manufactured by the assignee of this invention, was an early attempt to use a direct drive, solenoid actuated, compound valve. At first blush and in principal, it would appear quite similar to the valve of this invention except that it was a 4-way, 4-land hydraulic valve. The valve was not very producible and required extensive customizing and bench tuning of each valve. No known compound pneumatic valves have been developed which function in the 0.5 to 2.0 horsepower range having bandwidths of 30 to 45 Hz.
It is an object of the present invention to provide a compound pneumatic valve for operation with a balanced actuator capable of controlling up to 2 horsepower with a bandwidth of 30-45 Hz for driving a missile control surface or motor nozzle with no increase in the number of control solenoids and electrical drive circuits required for an unbalanced actuator scheme.
It is a further object of the present invention to provide a compound pneumatic valve which maintains essentially constant bandwidth with increasing horsepower.
A still further object of this invention is to provide a valve which can be scaled to accommodate a range of flows or what might be referred to as horsepower without big changes in the valve configuration while maintaining response characteristics and thereby avoiding degradation in bandwidth.